Brain reperfusion may be of particular importance in the etiology of periventricular leukomalacia, of which the common findings are gliosis and ventricular dilatation. To investigate the mechanism of this pathogenesis, we used a metabolic inhibition (MI) model using cyanide plus deoxyglucose treatment of cultured glia isolated from fetal rat brain and examined the activity of extracellular signal-regulated protein kinase (ERI) during MI and also during the recovery from MI of 30 min. ERK activation was stimulated during MI and the recovery from MI. The time course and extent of activation of ERK during Ra and the recovery from MI, however, were distinctly different. Activation of ERK was stimulated within 5 min of MI and declined thereafter. Activation of ERK was sustained during the recovery phase from MI and the extent of the activation was much greater than that during MI. Pretreatment with EGTA to eliminate extracellular Ca2+, or with APV, an NMDA receptor ant agonist, to inhibit Ca2+ influx through the NMDA receptor, attenuated the activation of ERR Moreover, pretreatment with PMA to downregulate PKC abolished the activation of ERR. PD98059, an inhibitor of ERK kinase, attenuated the cell proliferation induced by MI followed by recovery from MI. These results suggest that ERK is involved in gliosis during the recovery phase from MI and may play a role in the etiology of periventricular leukomalacia.